The use of combination vaccines in the routine childhood program reduces distress to the recipients and is likely to improve uptake rates and timeliness of vaccination but requires careful evaluation and surveillance. The aim of this study was to evaluate the immunogenicity and reactogenicity of two commercial diphtheria-tetanus- acellular pertussis-hepatitis b-inactivated polio virus-Haemophilus influenzae type b (DTaP-HBV-IPV/Hib) combination vaccines when administered to infants at 3, 5 and 11-12 months of age. A total of 494 infants were randomized to receive three doses of either Infanrix hexa (GlaxoSmithKline Biologicals; N = 246) or Hexavac (Sanofi Pasteur MSD; N = 248) in 10 centers in Italy, Finland and Sweden. After the third dose, antibodies to diphtheria, tetanus, polio and Hib were at the protective level in nearly all infants in both groups whereas the proportion of subjects who had achieved the protective concentration of >or=10 mIU/ml to hepatitis B surface antigen was 99.1% (95% CI 96.7-99.9) in the Infanrix hexa group as compared to 94.4% (95% CI 90.4.97.1) in the Hexavac group. Antibody titers to all three polio antigens were highest in Italy and lowest in Finland. Clinically relevant general reactions (such as fever of >39.5 degrees C) were mostly reported in less than 5% of the vaccinees. Three doses of DTaP-HBV-IPV/Hib combination vaccines produced sufficient immune responses in nearly all vaccinees.